[PATCH] D133083: [support] Allow TimeProfiler tracing across threads

[Mark Shields via Phabricator via llvm-commits]

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This change allows a TimeProfiler profiling entry to be created
on one thread and finished on another. This was triggered by a use
case where we needed to trace the scheduling delay for work items
ultimately handled by independent worker threads.

The clock is changed to std::chrono::high_resolution_clock, both for
its increased precision (our work items can be in the us range), but
also for its cross-thread consistency (all threads see the same clock).

As a pleasant side effect it is now possible to pay for the cost of
constructing a profiling entry with a possibly expensive detail string
outside of the critical section we wish to trace. I think we could do
better with shifting the cost of constructing detail strings to the final
trace writing phase, given the API already supports providing detail
strings via a callback. But I've not audited the code to check if
detail closures could have their lifetimes safely extended so dramatically.

Could not find unit tests, please let me know if I missed them.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D133083

Files:
  llvm/include/llvm/Support/TimeProfiler.h
  llvm/lib/Support/TimeProfiler.cpp

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